Melanocortin receptors belong to the rhodopsin sub-family of G-protein coupled receptors (GPCRs). Five different subtypes are known. These melanocortin receptors bind and are activated by peptides such as α-, β, or γ-melanocyte stimulating hormones (α-, β-, γ-MSH) derived from the pro-opiomelanocortin (POMC) gene. A wide range of physiological functions are believed to be mediated by melanocortin peptides and their receptors.
U.S. Pat. No. 5,532,347 (issued Jul. 2, 1996) to Cone and Mountjoy discloses human and mouse DNA molecules which encode MC-1R (also known in the art as α-MSH-R). The expressed human protein contains 317 amino acids.
U.S. Pat. No. 5,280,112 (issued Jan. 18, 1994) and U.S. Pat. No. 5,554,729 (issued Sep. 10, 1996), both to Cone and Mountjoy, disclose human and mouse DNA molecules which encode MC-2R (also known in the art as ACTH-R). The human MC-2R protein contains 297 amino acids.
Mountjoy, et al. (1992, Science 257: 1248–1251) describe DNA molecules and the concomitant protein for human MC-1R and human MC-2R.
Chhajlani, et al. (1992, FEBS Letters 309: 417–420) also disclose a human DNA molecule comprising an open reading frame which encodes human MC1-R.
Roselli-Rehfuss, et al, (1993, Proc. Natl. Acad. Sci 90: 8856–8860) disclose a cDNA clone encoding rat MC-3R cDNA.
U.S. Pat. No. 5,622,860 (issued Apr. 22, 1997) and U.S. Pat. No. 5,703,220 (issued Dec. 30, 1997) to Yamada and Gantz, disclose DNA molecules which encode human MC-3R and human MC-4R, respectively (see also Gantz, et al., 1993, J. Biol. Chem. 268(11): 8246–8250).
A DNA molecule encoding human MC-5R was also disclosed by Mountjoy, et al. (1994, Mol. Endocrin. 8: 1298–1308).
Chhajlani, et al. (1993, Biochem. Biophys. Res. Comm., 195(2): 866–873) disclose a DNA molecule which the authors state encodes MC-5R. This clone was initially designated MC2.
Fathi, et al. (1995, Neurochemical Research 20(1):107–113) also disclose a DNA molecule thought to encode human MC-5R. There are several sequence discrepancies when compared to the DNA molecule disclosed by Chhajlani, et al., id.
Griffon, et al. (1994, Biochem. Biophys. Res. Comm., 200(2): 1007–1014) disclose DNA clones from human and rat which encode MC-5R. The human DNA sequence agrees with the human DNA sequence disclosed in Fathi et al. id.
Gantz, et al. (1994, Biochem. Biophys. Res. Comm., 200(3): 11214–11220; see also U.S. Pat. No. 5,710,265, issued Jan. 20, 1998 to Yamada and Gantz) and Labbe, et al. (1994, Biochemistry 33: 4543–4549) disclose DNA clones from mouse which encode MC-5R.
Barrett, et al. (1994, J. Mol. Endocrin. 12: 203–213) disclose DNA clones from sheep which encode MC-5R.
In rodents, MC-4R has been implicated as a key regulator of feeding behavior which regulates body weight through studies with peptide agonists and antagonists (Fan et al., 1997, Nature 385: 165–168) and with a MC-4R knock-out mouse (Huszar et al., 1997, Cell 88: 131–141).
Compounds that bind to such receptors were previously identified by binding to human and/or rodent receptors and evaluated for their efficacy in rodents. However, the neuroendocrine process can differ between rodents and man. It is also expected that some compounds exhibit different binding affinities for different species homologues of the same receptor (Fong et al., 1992, J.Biol. Chem. 267:25666–25671; Hartig et al., 1992, TIPS 13:152–159).
Before compounds can be selected as a drug candidate it is first evaluated for a physiological effect in rodents and then in the rhesus primate. It is often that one compound may be effective in one animal species but not in another. Previously, it has been impossible to determine if the failure was due to an altered melanocortin pathway in different species, or due to a compounds having a lower affinity for one particular species. Past protocols required the use of a rhesus brain membrane to determine the in vitro biochemical activity of compounds, if such protocol could be successfully employed.
It is desirable to correlate in vivo data with in vitro biochemical activity of compounds.
It is also desirable to first select compounds that are active for the rhesus receptor in vitro.
It is also desirable to identify compounds which can determine the relevance of receptor targets in rhesus and allow selection of novel drugs to treat obesity.
It is further desirable to discover new drugs which effect pathophysiological processes by modulating the effects in rhesus to identify melanocortin active process in primates, followed by human clinical trials.
The present invention addresses and meets these needs by disclosing an isolated nucleic acid fragment which expresses a form of rhesus MC-4R, recombinant vectors which house this nucleic acid fragment, recombinant host cells which expresses rhesus MC-4R and/or a biologically active equivalent, and pharmacological properties of this rhesus MC-4R protein.